Studies on the physico-chemical parameters and plankton abundance in relation to fish productivity were carried out on four natural lakes in the four agricultural zones in Anambra State, Southeastern Nigeria. Data were collected during two seasons (wet and dry) and statistically analyzed. Emerging results obtained from the study revealed an inverse relationship between phytoplankton and zooplanktonabundance. In all the four lakes, plankton density as well as physico-chemical parameters varied with the seasons, being more abundant in the rainy season. Four major families of phytoplankton viz: Chlorophyceae, Baccillariophyceae, Euglenophyceae and Cyanophyceae were identified in the course of the study. Four major classes of zooplankton viz: Cladocera, Copepoda, Ciliata and Rotifera were also identified in the four lakes.Low densities of plankton were recorded in February and March while high densities were recorded in August and September. Generally, the phytoplankton out-number the zooplankton. Fifteen families of fish were identified viz: Osteoglossidae, Cichlidae, Characidae, Hepsetidae, Citharinidae, Distichodontidae, Cyprinidae, Centropomidae, Clariidae, Bagridae, malapteruridae, Channidae, Pantodontidae, Mochokidae and Schilbeidae. Agbu lake had the highest fish productivity followed by Obutu Lake and Agulu lake. There was no evidence of fisheries activities in Nwangene Lake. Fish species encountered in Nwangene Lake were of no commercial importance. Potential fish yield in Agulu Lake (mean depth 5.50m) was 2.32%; 3.40% from Agbu Lake (mean depth: 3.50m); 3.80% for Obutu (mean depth: 3.20m) and 9.86% for Nwangene (mean depth: 1.25m). Thus there existed a general trend of increasing productivity with decreasing with decreasing depth which is an illustration of the principle that biomass is not necessarily correlated with rate of production.
Keywords : Natural Lakes, Physico-Chemical Parameters, Plankton Abundance, Fish Productivity.